Clinical report of microsurgical treatment of Kohler's disease

The conservative treatment for Kohler's disease will take several months, but some patients still have flatfoot and persistent pain. From October 2013 to July 2015, 3 children with Kohler's disease underwent navicular decompression and micro-circulation reconstruction surgery in our hospital. All the patients have received conservative treatment for more than 3 months and the effect was poor. X-ray showed the bone density of navicular increased significantly. All patients were followed up over 1 year. The 3 patients recovered well. VAS score decreased from 7.0 to 2.6 at 1 month after the operation. The pain symptom disappeared completely on 3 months after surgery. The density of navicular bone recovered to normal. Navicular decompression and micro-circulation reconstruction surgery may quickly improve the ischemic status of navicular bone, alleviate pain symptom and enable patients to resume normal activity as soon as possible.


Pre-and post-operative assessment
All the patients underwent physical examination and X-ray before and after the operation.2 patients had MRI examination before the operation.

Surgical procedure
The patients were operated in supinate position under general anesthesia with a tourniquet on the thigh.Anterior-medial approach was used, and the incision was from the tip of the medial malleolus to the distal of the cuneonavicular joint.The extensor hallucis longus tendon and extensor digitorum longus tendon were retracted, and the dorsalis pedis artery and the medial tarsal artery were exposed at the talonavicular joint level.
The medial tarsal artery was dissociated about 3 cm.The navicular was exposed and a 2-3 cm deep hole was drilled on the dorsal side with a 3.0 mm drill for decompression.Care was exercised to not drill through the contralateral cortex to prevent excessive damage and bleeding.The medial tarsal artery was cut off, the distal part of the vessel was ligated and the proximal end was kept open, and blood flowing from the artery and accompanying veins could be seen.The opened proximal end was inserted into the drilled hole of the navicular.The medial tarsal artery was fixed on the periosteum of navicular by absorbable suture.The incision was closed and the foot was fixed in the neutral position with splint.The surgical procedure was shown in Fig. 1.

Postoperative treatment
The affected feet were fixed with splint for 3 weeks.The patient began weight-bearing stand training at 4 weeks after operation, walk slowly and gradually return to normal walking.

Follow-up
The patients were followed up once a month after the operation to check whether their feet have swelling, pain or infection.X-ray check were taken every month within 3 months after the operation.After 6 months, the foot condition was checked every 3 months, the epiphyseal closure, foot arch development and local symptoms were recorded.

Ethical approval and Informed consent
This study was approved by the Ethics Committee of Qilu Hospital of Shandong University.All procedures performed in this study involving human participants followed the relevant guidelines and regulations of the Declaration of Helsinki.All patients in our study were anonymous.Informed consent was obtained from all individual participants included in the study.

Results
The 3 patients recovered well after the navicular decompression and micro-circulation reconstruction surgery.VAS score decreased from over 7 preoperative to 2.6 at 1 month after the operation.There was no pain and tenderness on their foot at 3 months postoperative.All patients had noticeable radiography improvement at 2 months, and radiographic recovery at 3 months.All patients resume normal walking within 2 months after surgery.The density of navicular reduced, normal trabecula pattern recovered, the shape of navicular became normal.(Fig. 2) All patients resume normal activities at 3 months after the surgery.Until the last follow-up, no recurrence was recorded, and the navicular developed naturally, same as the contra lateral (Fig. 3).

Discussion
Kohler's disease is believed to be a self-limited disease, but conservative treatment usually need several months, and sometimes may lead to failure.Conservative treatment include controlled ankle motion boot, crutches, short leg cast and drugs.Conservative treatment is the first choice of patients and doctors, but it is very difficult for young patients to cooperate with long-term external fixation.We need to find ways to quickly and thoroughly solve the problems.The vascularized bone transfer in the form of the medial femoral condyle free flap was a valuable method for navicular avascular necrosis 10 , but need microsurgical technique and vessel anastomosis.Core decompression have demonstrated favorable outcomes in treatment of Kienböck disease and scaphoid necrosis 11 .But these method had never been used in treat the Kohler's disease.We performed navicular decompression and micro-circulation reconstruction on 3 patients, and the results showed that the course of treatment was short, and the curative effect was definitive.But surgery also carries the risk of foot scars and tendon adhesion.
The etiology of Kohler's disease remains unclear.As the navicular on the top of the medial arch, and under great stress among the talus and cuneiform 10,12 .Moreover, the ossification center of the navicular, which is the latest, may be affected by the stress and lead to the avascular necrosis of the navicular bone 13,14 .Drill on the  www.nature.com/scientificreports/bone may reduce the internal pressure.Core depression had been used in treat the wrist scaphoid nonunion and get good results.The vascular implantation would restore the blood supply, helping the navicular bone recover from avascular necrosis.Reconstruction of micro-circulation with vascular implantation has long been used in treating bone ischemic necrosis 15 , but never been used in the treatment of Kohler's disease.Compared with free vascularized bone transfer, vascular transplantation is a more direct and comfortable operation.Besides oxygen and nutrition, the vascular implantation also brings growth factors and fibroblasts or other cells, as the foundation for bone reconstruction 16 .
We also need to note that despite surgery, there also could be a spontaneous effect of improvement related to rest and cast treatment.In our study, the affected feet were fixed with splints for 3 weeks, which was shorter than conservative treatment.More comparative studies were needed in the future to clarify the effectiveness of surgical treatment.

Conclusions
Navicular decompression and micro-circulation reconstruction by vascular implantation to treat Kohler's disease, the results showed the sclerotic bone quickly recovered and the symptoms alleviated.Though more cases observation are needed, we believe this procedure might be an promising treatment method.The indication for surgery is only patients with severe pain and after failed conservative therapy of several months.

Figure 1 .
Figure 1.The surgical procedure of vascular bundle implantation to treat Kohler's disease.(A) Located the navicular under fluoroscopy; (B) Drill under fluoroscopy; (C) and (D) Exposed the dorsal pedal artery and the medial tarsal artery at the talonavicular joint level; cut the medial tarsal artery and accompany veins, (E) Showed bleeding of the proximal end(Arrow); (F) Vascular bundle implantation into the drilled hole of the navicular.(Arrow).

Figure 2 .
Figure 2. Case 1 radiography changes of the navicular after vascular bundle implantation.(A) Pre-operation X ray showed navicular bone sclerosis; (B) Pre-operation MRI showed ischemic status of the navicular bone; (C) 1 month post-operation X ray showed radiography improvement of the sclerotic navicular bone; (D) 3 months post-operation X ray; E, 6 months post -operation X ray.

Figure 3 .
Figure 3. Case 2. (A) Pre-operation X ray showed the right navicular bone sclerosis,compared with the left foot; (B) Pre-operation MRI showed ischemic status of the navicular bone; (C) 1 month post-operation X ray showed radiography improvement of the sclerotic navicular bone; (D) 2 months post-operation X ray; (E) 7 years post-operation X ray.